1. Field of the Invention
The present invention relates to a method for preparing focus-adjustment data for a focusing lens system of an optical defect-inspection apparatus, and a focus-adjustment wafer used in such a method. Also, the present invention relates to an optical defect-inspection apparatus which is constituted so as to carry out the method.
2. Description of the Related Art
Conventionally, there are various types of optical defect-inspection apparatus for inspecting a semiconductor wafer to detect defects on each of the semiconductor chips on the semiconductor wafer, as disclosed in, for example, JP-2003-271927 A.
The optical defect-inspection apparatus includes an optical image sensing unit for optically sensing each of the semiconductor chips to thereby produce chip image data, and an image-processing unit for electronically processing the chip image data to thereby detect defects on the semiconductor wafer based on the processed image data.
Also, JP-2000-058606 A discloses a reference wafer used in a light-scattering inspection apparatus to detect and quantify scratch defects which are made in a semiconductor wafer when the silicon wafer is subjected to a chemical mechanical polishing (CMP) process. Namely, the reference wafer has a plurality of dummy scratch defects formed in a surface thereof, and each of the dummy scratch defects has known width and depth. The dummy scratch defects are previously optically sensed by using an optical scanning unit of the light-scattering inspection apparatus to thereby acquire width and depth data on each of the dummy scratch defects.
When the semiconductor wafer subjected to the CMP process is inspected in the light-scattering inspection apparatus to detect scratch defects, each of the detected scratch defects is compared with the width and depth data of the dummy scratch defects to thereby quantify the detected scratch defect concerned.
At any rate, the optical defect-inspection apparatus and the light-scattering inspection apparatus have an optical scanning system for scanning a semiconductor wafer with a light beam, and the light beam is focused on the semiconductor wafer by using an optical focusing lens system. Namely, the semiconductor wafer is positioned in place with respect to a focal plane defined by the optical focusing lens system.